This invention relates to permanent magnet motors and, more particularly, to a method of constructing such a motor and a motor field assembly constructed by such method.
In the past, it was common to form a motor shell for a permanent magnet motor by deep drawing relatively thin sheet stock into a cup-shaped configuration. With the advent of higher strength magnets, this thin sheet stock material has been found to have insufficient flux carrying capability. However, thicker sheet stock material cannot be deep drawn. Schmitt et al U.S. Pat. No. 4,309,815 discloses a motor housing for a small motor wherein the cylindrical wall must be of a certain thickness. This wall is formed by providing a sheet metal band which is bent on a mandrel, on top of which is bent a sheet metal strip, so that the combined thickness of the band and the strip satisfies the wall thickness requirement. This construction is disadvantageous in that it requires two pieces of material for forming the motor shell, both of which require a forming operation. It would still be desirable, however, to manufacture the motor shell out of sheet stock, for reasons of economy. Accordingly, it is an object of this invention to provide a method of motor construction which utilizes sheet stock material of sufficient thickness for carrying the flux of high strength magnets.